With the advancements in image processing technologies and information processing apparatuses, there have been proposed various techniques for generating images and techniques using image analysis. In particular, a technique for extracting the contour of an object is a key technique in a wide range of fields, including visual tracking, computer vision, medical image analysis, and retouching. Since the contour of an object in an image can be regarded as part of edges, an edge extraction filter is often used for the extraction of contours. For example, in the Condensation (Conditional Density Propagation) algorithm for visual tracking techniques, a finite number of particles are used to provide an existence probability distribution of a tracking object, and matching is performed between a candidate contour, which is specified by a particle and has the same shape as the tracking object, and an edge image so as to observe the likelihood of each particle and estimate the existence probability distribution of the next frame (see Non-Patent Literature 1 or 2, for example).
Meanwhile, as a technique for extracting a contour, there have also been proposed active contour models (Snakes) with which a contour model of an object is represented by a closed curve, and such a closed curve is changed so that a predefined energy function becomes minimum, thereby estimating the contour of the object (see Patent Literature 1 or 2).